1. Field of the Invention
This invention relates to a system for indicating a receiving channel number for a television receiver.
2. Description of the Prior Art
In the prior art receiving channel number indication systems for the television receiver, regardless of whether the means for varying the local oscillation frequency of the tuner includes means for mechanically changing over connection of a coil or a capacitor, or uses a varactor diode, the correspondence between the receiving frequency or the local oscillation frequency and the receiving channel number is attained by the correspondence between a contact or memory means and the receiving channel number.
This is for selecting a receiving channel number not by use of a receiving frequency or a local oscillation frequency but by use of the location of the contact or memory means. First of all, therefore, it is necessary to define or preset the relation between the local oscillation frequency and the receiving channel numbers. If a contact (or memory means) is located at a, for instance, the local oscillation frequency for receiving the channel 2 is preset at the location a. If the local oscillation frequency for receiving the channel 3 is preset at the location a, on the other hand, a different channel is received at the same location. Thus, it is not that the location a has data "2" of the receiving channel number specific to the location a, but the particular location corresponds to the channel number "2" in view of the fact that the location a is defined as the channel number "2." Exactly speaking, in this conventional indication system, it is not a channel number but merely a selected position of the channel selector that is indicated. Thus, this conventional indication system has the disadvantages mentioned below.
(1) Even when the indication system indicates "2" it is not exactly known whether the television receiver really is receiving the second channel. The right indication is obtained only when the local oscillation frequency is preset to receive the channel Nr. 2 at the associated selected position of the channel selector. If the presetting is incorrect, therefore, the indication system erroneously functions.
(2) There is no correlationship between the selected position of the channel selector itself and the receiving frequency, and therefore the presetting is always required to achieve the correlationship.
(3) In the case of auto-presetting wherein the presetting is performed automatically but not manually by receiving a broadcast signal, or in the case of auto-search receiving wherein the tuner automatically searches for a broadcasting station, the relation between the local oscillation frequency and the receiving channel number is not preset in advance and therefore it is not possible to indicate the channel number of the broadcasting station involved.
An example obviating the disadvantages (1) and (2) above is shown by a UHF detent tuner disclosed in U.S. Pat. No. 3,842,683. Since this requires a purely mechanical fine adjustment of tuning variable capacitor, however, the accuracy in manufacture thereof or applications to a VHF tuner or auto-search or auto-presetting pose a problem.